Production of selenomercaptans



Patented June 6, 1950 STATES PATiiN'll oli-FICE .Y 2,510,765wf pf w i Y ERODUCTION. 0FV sELENoMEiiCAPTA-Ns Willialn T.:Ss'ewart, Berkeley, Galifi; aissignio to California Research Corporation, San Fran'- oisco, Calih, a corporation of Delaware No Drawing'. Applieetionlviay la, 1946,.

i serialNe. 669,467

7 claims.- (ol. 26o-429) "This lnventionrela-tes 'toa new and useful method of preparing seleliomeifcaptas vand salts lia-ve utility' inferir'ieuiiites'4 iii viii-e preparation 'y'f'otli'ler"corpolil'iiV of selenium-.f Salts of the selenoinerieptafisf eoiitaifi g1 not les's- 'than live, piiefeialely eight te thirty ee'rpeii eterni" iii the aliphatic redieel'etiazerieuf te selenium, faire`4 else veiliifable einiieiiidanisifer mineral lubricating-oils and the' like; Polyvalent iiietulA salts; of tl'iese fiitielseleiienieieaiitaiis lelfe' useful as' inotoie i' d ergents5f`i. additives tdprdriiete eng'ie'eleanliness' and to inhibit piston ring sii'eiiiiiie.l

' estre ueserib'eci in trie literature for 'prepari-iig; lipl'iaticseleiioiiieicailtimf einel by ifeaetiei of sodium-er magnesium* liydroseleide [Neri-Se eif'MgfiHseiifl with r 'an'- aliplfietie melide er "aliena-tie'iiietel sulfate, er ley` retienen -of is elieiiaieter'izeuffby e goedyieldV of seleiidiiieiee'pteii ena @minimum of Siae feee'iiei'is" ao iiiiwiirited products.V

lt le a. particular em'ei fiiiisfinveiiiieii te provideV e. simple; eeeiieiiiieel iiii-stliielv oi prepaiing ,l'iig'li, inele'eiila weight elio-natie selenoiiiee eepigiiis 'eiid Seite' fille (sente i-iing' eiglii 6r mere carbon eioiiiein Elie: liyiiieaiterad-il, wiieli 'aiifoiiisth use' friyaro'geiiseleiiide, previdesl e goed yield of 'seleriefiieiceipien and yields pro'duet viii-eli een be purified without disiillfee 1011.y

It isa further part'izll'-l" jct "oi` the invention to provide a meeiis oi pfiliieiiig ifieeiil sans of Seleiiem isi-,eine by sifiiple r6-euere involvingl reduction ieee-ily eiveilebl'e selenium eeiiiiieiiiiel' aiidrlfeeiefy oi ineeesiredfiiieiel salt f therea'tien prod-uet iifitliiiut isol'eiting'v engi lnterniedla Ythis "can-l Be" conveniently" accomplished by nuiiiithfany suitable" heisev cti'peible" of forming more 3 added. After completion of the reaction, the product is treated in either of two ways, depending upon whether dodecyl selenomercaptan (n-C12Hz5SeH) or zinc dodecyl selenomercaptide [(nC1zH25Se)zZnl is desired:

(a) If dodecyl selenomercaptan is desired, the reaction mixture is extracted with ethyl ether and the solvent evaporated on a steam bath.

(b) If zinc dodecyl selenomercaptide is desired, the reaction mixture (after filtration, if necessary, to remove solid impurities), is neutralized with caustic soda solution, whereupon Zinc sulfate dissolved in the aqueous layer causes precipitation of zinc dodecyl selenomercaptide, probably by the series of reactions:

The method of the invention is especially advantageous in the preparation of high molecular weight aliphatic selenomercaptans, those containing eight or more carbon atoms in the molecule, and their salts with polyvalent, reducing metals. A minimum of by-products are produced. If it is desired to recover the selenomercaptan, this can be done by physical means as in embodiment (a), above. If it is desired to recover a zinc or other polyvalent, reducing metal salt, this can be done by embodiment (b), above. In either case, the necessary steps of recovery are reduced to a minimum and distillation of the product is made unnecessary.

By aliphatic radical as used herein and in the claims is meant a radical attached to selenium by a non-benzenoid carbon atom. Thus, benzyl selenocyanate, lauryl selenocyanate and cyclohexyl selenocyanate are all aliphatic selenocyanates, and upon reduction yield aliphatic selenomercaptans, within the meaning of the term aliphatic as used herein and in the claims.

The reduction of the selenocyanate, as stated, is carried out by means of a metallic reducing agent in an acid medium. The preferred reducing agent is zinc, which may be in any suitable form, such as mossy zinc or zinc dust. Of the two, zinc dust is preferred. Examples of other suitable reducing agents are aluminum, magnesium and iron.

The preferred acids for rendering the reaction medium acid are sulfuric acid and hydrogen chloride. Acetic acid may be used as may other organic and inorganic acids.

The reaction medium will usually comprise a solvent, such as water, alcohol, acetone, ethyl ether or dioxane, but in the case of acetic acid, glacial acetic may be used, functioning both as the source of hydrogen and as the reaction medi- The concentrations of acid used and the manner of conducting and controlling the reduction reaction Will vary according to the acid used and considerations of convenience. Thus, where suluric acid is used, an aqueous solution of to 70% concentration may be used, 40 to 60% being preferred. In such case, the selenocyanate is preferably mixed with the aqueous acid, held at an elevated temperature or under reflux, and agitated while the reducing agent is added gradually, at such rate as to control the reaction. However, it is possible, though less desirable, to add zinc and selenocyanate to Water, hold under reflux and agitate and gradually add concentrated sulfuric acid.

Where hydrogen chloride is Used, the 50h/ent or reaction medium is preferably alcohol. The selenocyanate and zinc are preferably added to the alcohol and the mixture is refluxed and agitated while gaseous HC1 is passed into it. By controlling the rate of addition of HCl gas, the reaction can be controlled. Preferably, the reaction mixture is kept saturated with HC1, but concentrations as low as 10% may be used. Variants of this embodiment of the invention Will be apparent to one skilled in the art.

Where acetic acid is used, it is preferably used in the same manner as sulfuric acid, concentration of the aqueous solution preferably being 20 to but, as stated, even glacial acetic acid may be used.

It will be understood that in cases Where the whole body of acid is added before the start of the reaction, the acid concentration will diminish as the reaction proceeds. Also, While reuxing temperatures are preferred, lower temperatures, usually to 260 F., depending upon the solvent, may be employed.

Frequently, where a metallic reducing agent, such as zinc dust, is added to a heated mixture of acid medium and selenocyanate, the reduction will not have'been completed upon adding all the reducing agent. In such cases, it is expedient to add a further quantity of acid and continue heating or reuxing and agitation until the reduction reaction is completed or substantially completed.

Thereafter, the product is Worked up as indicated. If the selenomercaptan produced by the reaction is liquid, it will separate out as an oily layer; or if a solid, as a crop of crystals upon cooling. This oily layer or crop of crystals can be recovered by decantation, filtration or ex.- traction with a solvent, such as ethyl ether, petroleum thinner or benzene. It can be used as such, e. g., as an antioxidant, or it can be purified as by fractional distillation; by recrystallization from a solvent such as a mixture of benzene and acetone or benzene and ethyl alcohol; or by treating it with aqueous caustic alkali, adding to the resulting aqueous solution or dispersion an aqueous solution of a polyvalent metal salt (such as Zinc acetate) to precipitate a polyvalent metal selenomercaptide and regenerating the free selenomercaptan from its polyvalent metal salt.

Alternatively, where the salt of the selenomercaptan and the reducing metal is desired, there may be added to the reaction mixture water (if the mixture is non-aqueous) and a neutralizing agent such as sodium or potassium hydroxide, sodium or potassium carbonate, sodium or potassium acetate or ammonia, in quantity sumcient to neutralize or substantially neutralize the acid. This brings about formation of a water-insoluble polyvalent reducing metal selenomercaptide (e. g., zinc selenomercaptide where zinc has been used as the reducing agent), Which can be recovered by filtration, dried and used as such (e. g., as a motor oil detergent) or puried, as by recrystallization from a suitable solvent such as a mixture of benzene and ethyl alcohol.

The following specific examples will serve further to illustrate the practice and advantages of the invention:

Example 1.--Peparatzon of Z-ethylheyl selenomercaptan and zinc salt thereof Z-ethylhexyl selenocyanate was prepared by reacting 1150 grams of crude 2-ethylhexy1 chloride with the calculated amount of potassium V selenocyanate :in i reduxing" 'alcohol y Fifteen hundredanrd eighty'grams .of the resulting crude ZFethylhexylr selenocyanate; vcontainling:v 5:3 mol-ies of 2-ethyll1exyl selenocyanate hissedv on selenium content, Vwere 'heatedand Vstirred at` FMP-i809 F. with-116101 imflf. rit-'50.1% y(ity '1W-eight) Vsulfuric acid. 7Six. hundred and nitty-lite grains otizine dust were added' iti-small: portions: over a, lperiod of minutes. When the addition was complete, 462 Vm1r of concentrated sulfuricaciddissolved in 1132.11mloiwate1r were added, the. vt:temperature was .increased to,- 210oA Fxand stirring was' continued for two hours. The cooledreactioru mi turewwas extracted with-i'petrolieum. 'etlrenthe extract was dried and freed'oil solvent. on; the steam v'loathe residue;y :crude: :Zeethylhexyl selenomercaptamwas purified andffthe zinc.. was prepared as. followlsi: The: crudeselenemereaptan wasstirr'ed' wit-hi 2130 Inli.V 'oi absolute iethyli alfcohol andi 556; grams: oil' acetate: dissolyed'in .21?1'0:v of: 'ho't. 50%- etnyl alcohol; were?` added slowlyrzY Avwhitef precipitate or Zinc 2fethylghexyl selerromercaptidei:formed and; was filtered. oit, washedfwith. acetone and ethyl?. alcohot and dried'. AnalysisA Found; Se=f3f1..6% 311.91%,A Zhf=`l3.9f%. Theoretical; Se`-` i2% -.,Y Zn=li.5;-%..k 'The'fproduct weighed 1152 grams, representing: a. yield:` of 901547; based ern-selenium. AAsan'rple of this Zinc 2-ethylhexyl selenomerca-ptide wasrdissolved in hot benzene'andl treatedi'with concentrated hydrochloric acid under nitrogen. The benzene layer was wasl'iediwtth-waten dried over anhydrous sodium sultate distilled.. Z-ethylhexyl selenomercaptan distilled atv 989-100? C. under a pressure ol. 30 mm. oil mercury. Analysis: Found, Se=40 .8`%;' theoretical, Se=40.8%. ND2"=1.4760.

Example 2.--Preparation of dodecyl seleneomercaptan and eine saltthereof Potassium selenocyanate was. prepared by dissolving'lo grams of metallic'seleniurrr a rs0- lution of 130 grams ofpotassiuni cyanidein 10'0 ml; otwater'.l 'After rem-oval 'of''the'iwater by heating at reduced pressure. 1000 ml.. of ethyl a-ll'- cohol and'A 48'1' grams ofcrude dodecyl chloride were added and the mixture Was stirred and heated at reflux for 27 hoursa The-product was extracted with petroleum ether, the' extract; was dried over anhydrous sodium sulfate and freed of solvent on the steam bath. The product (crude dodecyl selenocyanate) weighed 601 grams and contained 23.5% Se. Five hundred and ninety grams of this product were heated and stirred at 210 F. with 670 ml. of 50% (by weight) sulfuric acid. Two hundred and twenty grams of zinc dust were added over a period of 15 minutes. A mixture of 192 m1. of concentrated sulfuric acid and 470 ml. of water was added and stirring and heating at 230c F. was continued for one hour. After cooling, the product was extracted with ethyl ether and freed of solvent on the steam bath. 502 grams of crude dodecyl selenomercaptan assaying 25.5% Se were obtained. The crude product was purified and the zinc salt was prepared as follows: A solution of 198 grams of zinc acetate in 1000 ml. of ethyl alcohol was added slowly to a mixture of 490 grams of the crude dodecyl selenoalcohol and dried in vacuo over calcium chloride. Analysis Found: Se=23.3%; Z11=9.4%. Theoretical: Se=28.1%; Zn=11.6%. The prodi. was, inl fact,

uct weighed '5:25 gramsv representing avyiel'd' of 81% based ou selenium. A-sample of this. zine dodecyl selenomercaptidevwas dissolved in hot benzeneand treated with' concentrated hyd-rochloric acidunder nitrogen'. vThe henzenefl'ayer wasl washedw-ith ywater;*dried over anhydrous sodiumJsu-lifate and distilled.. The fraction( hoilfing between 160."and 'lfFGO at 101mm.' of mercury was collected.- .tnalysisz` Found: Se=3013%.=. Theoretical: Se=731'.6-%.` ND2=1./l74'1`..

Example :iL- Preparation 'of paranj .telecomercaiptmz n ,l A.

Y 'Par-fallin. sel'enocyanate was: prepared by reacting '553 grams 'of chlorinated match'vzax (a low melting point paraffin Wax, chlorinated tof10.6% C1) with"v the;- r'eaction product 'of -59;3gramsf of selenium andy 431% gra-ms of 'potassium cyanide; lihe reaction wasl carriedfou't irrreilxing, ethyl Cellosol-yfe. for 22. hours and thei'reactionlmixture was diluted with water and extracted with ethyl ether. Thefether extract wasidried over: sodium sulfate. filter-'edv and freed of. solvent. 'Thea weight of. the"` product was 628 'grams assaying 919% Se; representing a quantita-*tive yield.` of paraffin seienocyanate. VR;e'ductirsrr 'to2' the.` selenomer'capta-nfwas; carried'out. by passing a streamer' anzhydrous hydrogen chlorides'mtof a. remdhg' mixtureof 292vgrarns ofthel paraflin; selenocyanate, 52 grams.k of zinc dustandfiiZl) vmlfoi 05% ethyl alcohol over a` period oi oneheur and fertyminutesa!y The.-4 reaction f mixture4 was diluted with water, extractedfw-ithf petroleum ether andi the extract was dried with sodium sulfate, -ltered andfreedot szlylyentl"v Yield of produ-ctl was 265 gra-ms containing 8.01% seleniurml The product (para-fnfselienolnercantanli was. waxy andi'simila-rin Aappearancete. the original match;

:Selenomercaptans are prone toi'oxidat n by atmospheric foxyge'n. Ift is,therefore, advisable to blanket' reaction mixtures and solutions con-- taining nitrogen Gor' other inert gas) until'sueh time as'v the nal? product isobtained and: canf loev placed inl a closed container.Vv This done in the preparations' described above'. i ff Tl-rey method ofthe invention i's: applicable to the reduction of other selenocyanates te'selenoniercaptar-1s;x -e;v g), the-reduction off methyl; ethyl, n andV isopropyl,'n\--and seci-'loutyl, -n-"and sec.- amyl, nand sec.octyl, cetyl sec.heptadecyl, cyclohexyl, methyl-cyclohexyl, benzyl, phenyl and cetyl phenyl selenocyanates to the corresponding selenomercaptans.

The method of the invention is especially advantageously applied to the preparation of complex mixtures of aliphatic selenomercaptans (and salts of the same) such as prepared by chlorinating a mixture of petroleum hydrocarbons (naphtha, kerosene, lubricating oil fractions, paraffin wax), condensing the chlorinated product with sodium selenocyanate to produce a mixture of aliphatic selenocyanates and reducing the mixture to a mixture of aliphatic selenomercaptans. Such mixtures of petroleum hydrocarbons are predominately mixtures of paraflinic and/or naphthenic hydrocarbons; they have average molecular Weights ranging from 110, more or less, in the case of naphtha to 360, more or less, in the case of parafn wax. Some of these hydrocarbon mixtures, such as parain wax, are semi-solid or solid at atmospheric temperature; e. g., at 77 F.

Such mixtures may be chlorinated to any desired percentage of chlorine content, preferably about one gram atom f gram molecular weight of chlorinated mixture may be reacted with potassium selenocyanate to produce any desired degree of substitution of selenocyanate radical for chlorine. Ordinarily, about 40 to '70% of the chlorine will be substituted. Accordingly, the end product of the method of the invention (i. e., a mixture of high molecular Weight aliphatic selenomercaptans), will contain more or less chlorine according as replacement of the chlorine by selenium is more or less complete.

Other replaceable groups, e. g., bromine and other metal selenocyanates, e. g., sodium selenocyanate, may replace chlorine and sodium selenocyanate, respectively.

The method of the invention is especially advantageous as applied to preparation of such complex mixtures of high molecular weight aliphatic selenomercaptans (and salts of the same), since the desired product is itself a, complex mixture not readily adapted to purification by fractional distillation (except to isolate cuts boiling in a narrow range of temperatures), and the method of the invention provides a means of preparing such a mixture free or relatively free from unwanted by-products, such as aliphatic selenides and diselenides.

Thus, parain wax ranging in average molecular weight from about 300 to 400 can be converted in good yield by the method of the invention to a valuable mixture of selenomercaptans relatively free from other compounds of selenium.

In this and other similar embodiments of the invention, wherein the starting material is a complex mixture of hydrocarbon, which is then chlorinated, the amount of chlorine (or other replaceable group) in the nal product can be controlled in the second step of the reaction, i. e., the reaction of the chlorinated material with potassium (or other metal) selenocyanate. By using higher reaction temperatures or longer reaction periods, or both, a low chlorine product is obtained. Correspondingly, by using lower reaction temperatures and/or shorter reaction periods, a high chlorine product is obtained.

Iclaim:

1. A two-step process for the production of a substantially Water insoluble selenomercaptan chlorine per average the mixture, and the salt of a metal which comprises reacting said metal with an acid in the presence of an organic selenocyanate selected from the group consisting of the alkyl, cycloalkyl, alkaryl and arylselenocyanates and thereafter neutralizing the acidic reaction mixture with a base selected from the group consisting of the alkali metal hydroxides, the basic salts of the alkali metals, and ammonla.

2. The two-step process of claim 1 in which the selenocyanate is an alkyl selenocyanate.

3. The two-step process of claim 1 in which the metal is zinc.

4. The two-step process of claim l in which the acid is sulphuric acid.

5. A process for the production of selenomercaptans which comprises forming a mixture of an organic selenocyanate and an aqueous solution containing from 40% to 60% by weight of sulphuric acid and introducing into said mixture a metal reactive with said sulphuric acid, While the mixture is maintained at an elevated temperature, said organic selenocyanate being selected from the group consisting of the alkyl, cycloalkyl, alkaryl and arylselenocyanates.

6. The process of claim 5 wherein the metal employed is zinc.

7. The process of claim 5 wherein the organic selenocyanate is an alkyl selenocyanate.

WILLIAM T. STEWART.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,155,204 Prutton Apr. 18, 1939 2,398,414 Denison et al. Apr. 16, 1946 OTHER REFERENCES Borgstrom et al.: Journal of Amer. Chem. Soc., vol. 51, pages 3649, Dec. 1929.

Hofmann: Ber. Deut. Chem., vol. I, pages 177, 1868.

Lucas: Organic Chemistry (1935), page 319, American Book Co.

Ser. No. 416,912, Rath et al. (A. P. 0.), published April 20, 1943. 

1. A TWO-STEP PROCESS FOR THE PRODUCTION OF A SUBSTANTIALLY WATER INSOLUBLE SELENOMERCAPTAN SALT OF A METAL WHICH COMPRISES REACTING SAID METAL WITH AN ACID IN THE PRESENCE OF AN ORGANIC SELENOCYANATE SELECTED FROM THE GROUP CONSISTING OF THE ALKYL, CYCLOALKYL, ALKARYL AND ARYLSELENOCYANATES AND THEREAFTER NEUTRALIZING THE ACIDIC REACTION MIXTURE WITH A BASE SELECTED FROM THE GROUP CONSISTING OF THE ALKALI METAL HYDROXIDES, THE BASIC SALTS OF THE ALKALI METALS, AND AMMONIA. 